This invention relates to a linear scale measuring device for determining the amount of relative movement between two objects, and more particularly to a linear scale measuring device of the absolute type which is adapted to exhibit a correcting function with high accuracy.
In a machine tool or the like, it is highly important to accurately grasp or determine the amount of relative movement of a tool to a work. Also, in an industrial recorder other than a machine tool, accurate controlling of movement of a recording head relative to a record medium depending upon an signal input to the recorder requires to precisely measure the amount of relative movement between both.
In view of the foregoing, measuring systems of various types have been conventionally proposed as a means for measuring the amount of movement between two objects which are moved relative to each other. The proposed measuring systems are generally classified into an increment type for determining a relative value and an absolute type.
The increment type measuring system is adapted to measure the amount of relative movement between two objects or the relative position therebetween by means of a plurality of linear indented lines (increment data) formed in parallel with one another on a glass scale. Thus, the increment type measuring system fails to detect the absolute position of each of both objects, therefore, the absolute type measuring system is substituted for the increment type one when it is required to detect the absolute position.
The absolute type measuring system is adapted to detect absolute data (absolute value code) formed on a glass scale wherein the absolute positions are represented by several bits, so that the absolute data are detected to measure the absolute positions. The absolute type measuring system has been widely used in a rotary encoder and the like.
The absolute type measuring system, as described above, can measure the absolute position corresponding to the scale.
However, the conventional absolute type measuring system or device requires to increase the dimensions of the indented lines in view of the size of a detector, an error in assembling of the device and the like, so that it fails to be used for a measuring device which is required to exhibit high resolution necessary to measure a micro-distance.